Conventionally, there has been a shank attaching structure capable of attaching and detaching, with one touch, a shank of a cutter to and from an arbor having a base end portion fixed to a drilling machine (a electric hand drill or a drilling machine). In the one-touch type shank attaching structure, the shank of the cutter can be attached to the arbor with one touch by means of an engagement mechanism provided between the arbor and the shank by only inserting the shank of the cutter upward into an opening portion formed on a lower face of the arbor.
In the one-touch type shank attaching structure, however, a ring-shaped member (sleeve) provided on the outer periphery of the arbor should be relatively rotated with respect to an arbor body when the shank is to be detached from the arbor. With such a structure, for example, there is a disadvantage that the shank drops down if something comes in contact with the ring by mistake during the rotation of the drilling machine. In such a structure, furthermore, it is necessary to grip the shank by one of hands and to grip and rotate a ring-shaped member provided on the outer periphery of the arbor by the other hand, thereby relatively rotating the ring-shaped member with respect to the arbor body in an ordinary detaching work. More specifically, when the work of detaching the shank is to be performed, both hands should always be used inevitably.
With the shank attaching structure, furthermore, a concave portion for accommodating a part of a ball acting as an engagement member to be projectable into the inside diameter side should be provided on the inner peripheral face of the ring-shaped member. The depth of the concave portion becomes deeper in one rotational direction (almost U-shaped as seen in a section), that is, the internal face of the ring-shaped member (sleeve) is processed and the depth of the concave portion is gradually changed. Therefore, a special machine tool is required and a machine work is difficult to perform. As a result, a manufacturing cost is increased. In the shank attaching structure, furthermore, a plurality of coiled springs with small diameters should be provided for springs to energize the ring-shaped members in the direction of the rotation on the internal face of the ring-shaped member against the direction of the rotation. Accordingly, an inclined hole for holding the spring should be formed on the inner peripheral face of the ring-shaped member and the outer peripheral face of the arbor body, and assembly should be performed with the spring held in that state. As a result, a very difficult work should be inevitably carried out. In particular, it takes plenty of time and requires labors for processing to form the inclined hole with a predetermined angle on the inner peripheral face of the ring-shaped member. Furthermore, the above-mentioned one-touch type shank attaching structure is complicated. Therefore, a coolant cannot be supplied from the inside to a cutting edge portion of the tip of the shank. Accordingly, the coolant should be supplied from the outer periphery of the tool. For this reason, the coolant should be scattered to perform a drilling work. As a result, there has been a drawback that the coolant contaminates the circumference of a portion to be drilled and is scattered over an operator.
The present invention has been made in consideration of the circumstances, and it is an object of the present invention to provide a shank attaching structure which eliminates the above-mentioned drawbacks.